1. Field of the Invention
The present invention relates in general to the field of information handling system optical drives, and more particularly to a system and method for reducing RF emissions associated with an optical drive laser diode High Frequency Modulation (HFM) signal.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Over time, information handling systems have packed increasing information processing capability in smaller housings. For example, the powerful information processing capability of portable information handling systems, also known as laptops, has encouraged greater numbers of consumers to rely on a portable system as a primary household system. One difficulty that has arisen from the increased processing power built within small or portable housings is the management of increased radio frequency (RF) emissions output by the more powerful processing components used in the systems. RF emissions interfere with surrounding electronic devices and are thus restricted to certain limits by national and international regulatory bodies. For this reason, RF emissions are typically suppressed with a number of physical techniques, such as bonding, shielding and circuit layout design. However, each of these physical techniques tends to increase the size and expense of an information handling system. RF suppression presents a significant challenge with portable information handling systems, which typically have reduced space to include shielding or rearrange circuit layouts.
One way to reduce overall RF emissions for an information handling system is to build the system with processing components that have reduced RF emissions. The optical drive is one example of a processing component that generates RF emissions. For example, semiconductor laser diodes typically use a High Frequency Modulation (HFM) signal that produces relatively high levels of RF emissions. The HFM signal is used to compensate for noise in the semiconductor laser diodes (LDs) by superimposing the HFM signal over normal laser drive current. The noise is produced in the optical drive's read channel due to laser mode switching that occurs, as an example, when a portion of the LD's output is reflected back into the LD. The HFM signal superimposed on the normal laser drive current has an amplitude sufficient to force the LD on and off with each cycle of the HFM signal. Because the LD presents a non-linear load to the HFM signal, the harmonic content of the current in the circuit can be quite high, producing substantial RF emissions. These relatively high RF emissions when combined with RF emissions from other components of an information handling system can cause failure to achieve regulatory limitations on RF emissions. Such failures increase system cost and delay design completion while RF emission issues are analyzed and corrective actions performed.